A user equipment to user equipment proximity service (English full name: Device to Device Proximity Service, D2D ProSe for short) has become a research subject of a 3GPP (English full name: 3rd Generation Partnership Project, Chinese: 3rd Generation Partnership Project) LTE (English full name: Long Term Evolution, Chinese: Long Term Evolution) system Rel. 12 (English full name: Release 12, Chinese: Release 12) system. When a physical layer (the physical layer is based on OFDM-MIMO, English full name: Orthogonal Frequency Division Multiplexing-Multiple-Input Multiple-Output, Chinese: Orthogonal Frequency Division Multiplexing-Multiple-Input Multiple-Output) of an LTE system is used to provide a user equipment to user equipment direct communication service, not only a service range of the LTE system is expanded, but also user equipment to user equipment D2D communication may be used by more users.
In an LTE D2D ProSe service, an application scenario is that UE is used to transfer data of another UE by using a UE to UE relay method, so as to increase a transmission distance.
In an LTE D2D system, when sending a D2D signal, UE needs to send scheduling signaling in an SA (English full name: scheduling assignment, Chinese: scheduling assignment) resource, and then send a corresponding D2D signal in a data resource pool. When a D2D terminal sends scheduling signaling in the SA resource, the scheduling signaling includes a destination address of a signal to be sent.
Referring to FIG. 1, FIG. 1 shows an LTE D2D system. An LTE base station and four UEs are shown in the system. If UE 1 needs to send a D2D signal, the UE 1 needs to send scheduling signaling in a corresponding SA resource, and send a corresponding data signal in a data resource pool matching the SA resource. The scheduling signaling sent by the UE 1 in the SA resource includes a destination address. Assuming that the UE 1 needs to communicate with UE 3, in this case, the destination address is an address of the UE 3.
If UE 2 is used to relay data sent by the UE 1, the UE 2 first needs to receive the data before the UE 2 sends the data. A delay occurs when the UE 2 relays a signal of the UE 1. In addition, when relaying the data sent by the UE 1, the UE 2 first also needs to send scheduling signaling in the SA resource, and then sends, in the data resource pool matching the SA resource, the signal that needs to be relayed.
When relaying data of the UE 1, the UE 2 also needs to send scheduling signaling in the SA resource, and the destination address in the scheduling signaling is also the address of the UE 3. If at this time the UE 1 needs to send another piece of data, the UE 1 needs to send another piece of scheduling signaling in the SA resource, and the destination address in the another piece of scheduling signaling is also the address of the UE 3. In this case, for UE x in FIG. 1, if the UE x participates in relaying of the another piece of data, the destination addresses of the two pieces of scheduling signaling received by the UE x in the SA resource are both the address of the UE 3. The UE x cannot determine a time sequence relationship between the two pieces of data sent by the UE 1, and therefore cannot distinguish the two pieces of data. Consequently, D2D communication cannot be normally performed.